The Internet Protocol (IP) Multimedia Subsystem (IMS) is an architectural framework for delivering IP multimedia services. Historically, mobile phones have provided voice call services over a circuit-switched network, rather than strictly over an IP packet-switched network. In recent years alternative methods of delivering voice or other multimedia services over IP have become available on smartphones, but they are not yet standardized across the industry. IMS is an architectural framework to provide such standardization. Moreover, IMS is intended to aid the access of multimedia and voice applications from wireless and wireline terminals. Wherever possible, Internet Engineering Task Force (IETF) protocols such as the Session Initiation Protocol (SIP), for example, are utilized to ease the integration of IMS with the Internet,